The in vivo administration of chemical carcinogens like the polycyclic hydrocarbons, 3,4-benzo (alpha) pyrene, 3-methylcholanthrene or dimethylbenzanthracene increases the activity of several mammalian hepatic as well as extra-hepatic microsomal enzyme systems capable of metabolizing their inducers as well as other foreign compounds (xenobiotics). The microsomal fraction of the adult rat kidney contains an aryl hydrocarbon (3,4-benzo (alpha) pyrene) hydroxylase system which can be induced 5- to 30-fold by a single dose of 3-methylcholanthrene or 3,4-benzo(alpha)pyrene; concomitant with this induced enzymatic activity is an increase in the content of cytochrome P-450K. The proposed research project will investigate the induction of aryl hydrocarbon hydroxylase activity and of the cytochrome P-450K-dependent mono- oxygenase system in the kidney microsomal fraction from rats of various age groups; sex differences in the induction process will also be studied in the various age groups. Enzymatic activities of the kidney microsomal electron transport chain, such as, NADH and NADH cytochrome c reductase, NADPH cytochrome P-450K reductase, and NADH and NADPH cytochrome b5 reductase will be determined before and after induction with the polycyclic hydrocarbons. The activities of certain enzymes will be measured by stopped-flow technique. Optical spectral and electron paramagnetic resonance (EPR) properties of the induced cytochrome P-450K in the different age groups will be determined with a dual- wavelength recording spectrophotometer and an EPR spectrometer, respectively. Finally, a study will be undertaken to solubilize and purify the induced cytochrome P-450K-dependent hydroxylase system in an enzymatically functional state utilizing modifications of the procedure of Lu, Junk and Coon (1).